The present invention relates generally to an improvement in an intake silencer (muffler) attached to an outboard engine of a boat, for example. More particularly, the invention relates to an intake silencer for an engine having a breather passage formed in the intake silencer for returning a blow-by gas and a filter for purifying the blow-by gas passing through the breather passage.
Various outboard engines are known in which a space defined in a cylinder head cover and a muffling chamber defined in an intake silencer are interconnected in gas communication by a breather passage so that a blow-by gas generated in the engines can be returned through the breather passage to an engine intake path. An example of such outboard engines is disclosed in Japanese Patent Laid-Open Publication No. HEI-8-93433.
A filter is placed on the breather passage in order to prevent mist in the blow-by gas and impurities such as lubricating oil in the cylinder head cover from entering into the gas to be returned to the engine intake path.
There are drawbacks, however, to placing a filter in the breather passage. For example, components used for the path can take up more space, there may be difficulty in securing a large enough space for the filter in a small outboard engine space, the filter may require a complex support structure, and a large engine cover, forming an outer part of the outboard engine, may be needed.
Furthermore, in the conventional breather passage, an outlet member on a cylinder head side is placed at a higher level, while an inlet member on the intake silencer is placed at a lower position. Because of a height difference between the outlet member and the inlet member, oil in the cylinder head can easily flow into the intake silencer, thereby causing the filter to get dirty and degrade rapidly.
In addition, operation for replacing an old filter with a new one must be performed in a small engine space of the outboard engine. Thus, there is a need to simplify the replacement operation.
It is therefore an object of the present invention to address the issues listed above by providing an arrangement that facilitates disposition and removal of a filter for removing impurities, such as oil in the blow-by gas passing through the breather space, without adversely affecting a small space within an outboard engine.
Another object of this invention is to provide an intake silencer for an engine that prevents the filter from getting dirty and degrading rapidly.
According to an aspect of the present invention, there is provided an engine intake silencer, communicating through a breather passage with a space defined in a cylinder head cover of an engine, for returning a blow-by gas generated inside the engine to an intake side of the engine, comprising: a main box unit formed by joining an upper half and a lower half unitarily; a connecting duct for connection to the intake side of the engine; an intake duct for bringing in outside air; and a filter for purifying the blow-by gas, the filter being held by the upper and lower halves within the main box unit communicating with the space defined in the cylinder head cover.
The filter can be placed within the intake silencer, whose main unit comprises the upper and lower halves, by fitting the filter into retaining parts formed on the upper and lower halves and joining the upper and lower halves. Because the filter is placed inside a chamber of the intake silencer which guides the blow-by gas to the intake side through the breather passage in the engine, that supplies new air to the intake side by introducing the blow-by gas to the intake silencer for returning the blow-by gas to the intake side, there is no need to create a filter retaining part in the breather passage, and a filter support structure is simplified. In addition, the filter for the blow-by gas in the breather space can be installed without adversely affecting a small space inside the engine.
In a preferred form, the upper half of the intake silencer has a filter retaining portion with an opening, the opening is closed by a lid connected via a connecting member to the lower half, and the filter is held between a retaining portion provided on a rear surface of the lid and a retaining portion provided on the lower half. As a result, the filter can be installed and removed by taking the lid that covers the opening of the upper half of the intake silencer and inserting or taking out the filter from the opening. Because the filter can be installed and taken out very easily, maintenance becomes easier. Also, the filter can be changed without involving the breather passage components. When the outboard engine of the boat is a vertical engine with vertically placed crankshafts and the intake silencer is placed on the upper part of the engine, the filter can be changed easily and rapidly by taking the engine cover off.
Preferably, the lower half of the intake silencer has a bottom with an opening formed at a part of the bottom, the opening is closed by releasably attaching thereto a bottom lid member from below, the filter is retained by a retaining portion provided on a top surface of the bottom lid member, and the bottom lid member has a connecting portion, provided on a part thereof upstream of the filter, for forming the breather passage. In other words, the filter may be put in place or taken out by attaching or removing the bottom lid from the opening made in the bottom of the lower half unit of the intake silencer. As a result, filter installation and removal becomes very easy, and maintenance involving filter exchange becomes easier. In addition, the filter changing operation can take place without involving the breather passage components. The filter changing operation can be performed easily and quickly by removing the engine cover, when the outboard engine is a vertical engine with a vertically placed crankshaft, and the intake silencer is placed on the top part of the engine. Because the bottom lid includes a retaining part for the filter, the retaining part holds the filter, and the bottom lid is placed from below, to close the opening in the lower half, by screwing on the bottom lid, the structures of the upper and lower halves themselves are also simplified. Furthermore, a connecting portion for forming the breather passage is placed at the bottom lid, and the connecting portion is connected to the cylinder head cover side with a breather tube to thereby simplify the process of forming the breather passage in the intake silencer.
Desirably, the breather passage of the intake silencer has an inlet disposed at a higher position, and the breather passage of the cylinder head cover has an inlet disposed at a lower position. Although the breather passage connects the inside of the cylinder head cover and the inside of the intake silencer in a communicating fashion, oil and other components are unlikely to go through the breather passage into the intake silencer, because the exhaust part at the cylinder head cover side is at a lower position than the intake part at the intake silencer. As a result, it is possible to prevent premature degradation of the filter, make the filter last longer, and avoid a need to change the filter too early. These advantages lead to cost reductions.